The desire to make quality carpets inexpensively has resulted in interest in various nonwoven fabric primary carpet backings. Since most nonwoven fabrics are notoriously weak they tend to make undesirable carpet backings. However some oriented films have sufficient strength at basis weights acceptable for use as primary carpet backings.
A number of workers in this field have attempted to make a nonwoven fabric from an oriented film suitable for use as a primary carpet backing. These efforts have taken a generally concurrent path. They all involve molecularly orienting a polymeric film by stretching to a degree suitable to induce spontaneous fibrillation, associating the stretched films so that the axes of orientation of the film layers are perpendicular to one another, and mechanically fibrillating the film before or after association. When such a primary carpet backing is tufted, the positioning of the fibrils between the tuft rows with orientation parallel to the fibrils is uncontrolled and non-uniform. As used herein, a film is oriented to the point of "spontaneous fibrillation" when penetration of the film causes splits to occur which extend out from the penetration parallel to the direction of molecular orientation.
U.S. Pat. No. 3,841,951 issued to Kim on Oct. 15, 1974 follows this same path with certain variations. A striated or ribbed film is oriented and then the film region between the ribs is fibrillated producing an open network of filaments interconnected by a plurality of fibrils. The filaments give the final product strength. Canadian Pat. No. 944,116 to Jones issued Mar. 26, 1974 also generally follows this same path. The associated layers are needle punched to produce a felt-like structure. Two U.S. patents to Johnstone, Nos. 3,484,916 issued on Dec. 23, 1969 and 3,428,506 issued on Feb. 18, 1969, disclose similar structures to that described by Jones. In addition British Pat. No. 1,437,179 to Tough issued on May 26, 1976 discloses a similar structure with fibrillation before tufting occuring due to the sewing of the oriented films together.
Although these structures perform adequately as carpet backings, they suffer from certain deficiencies. In particular they possess less than optimal strength and tuft registration.